1. Field of the Invention
The present invention relates to a Time Division Multiple Access (hereinafter TDMA) system radio used for mobile communications or the like, and more specifically to a dual mode system which can use, in a single handset, both a frequency Division Duplex (hereinafter FDD) system which uses different frequencies for transmission and reception in the TDMA system and a Time Division Duplex (hereinafter TDD) system which time-shares transmission and reception, and also relates to a TDD dual band system which switches a plurality of frequency bands in the TDD system.
2. Related Art of the Invention
Recently, with an increasing demand for mobile communication services such as vessel phones, plane phones, and train phones as well as car phones, portable phones, and the personal handy phone system, various types of communication systems have been proposed. One such system is a TDMA system which makes a plurality of mobile stations share a radio wave of the same frequency from a base station by time sharing.
With reference to drawings, a conventional dual mode system will be described which is based on the TDMA system and integrally accommodates the TDD system and the FDD system into a single radio. With reference to FIG. 4 which is a block diagram illustrating the radio, the radio part of the FDD system will be described first.
At the time of reception, the mobile terminal 102a of the mode changeover switch 102 and the mobile terminal 103C of the transmission-reception changeover switch 103 are switched to the terminal 102b and the terminal 103R, respectively. The high-frequency signal which has entered from the antenna 101 for both the FDD and TDD systems passes the mobile terminal 102a of the mode changeover switch 102, the terminal 102b, the mobile terminal 103C of the transmission-reception changeover switch 103, and the terminal 103R, selects the reception frequencies of 810-826 MHz of its own station at the high-frequency band filter 104, is amplified by the high-frequency amplifier 105. Then the amplified high-frequency signal is mixed with the local oscillation frequencies of 680-696 MHz which have been inputted by the converter 106 from the local oscillation unit 107 so as to be converted into an intermediate frequency of 130 MHz, demodulated by the demodulation unit 108, and as a result, a reception output is obtained.
At the time of transmission, the mobile terminal 103C of the transmission-reception changeover switch 103 is connected to the terminal 103T side. The carrier frequency of 260 MHz is digital-modulated in the modulation signal generation unit 109 by a QAM modulation or another method so as to be converted into transmission frequencies of 940-956 MHz by using the frequencies of 680-696 MHz inputted from the local oscillation unit 107. After passing the band filter 110, the modulation signal is amplified by the high-frequency amplifiers 111 and 112, passes the band filter 113, the terminal 103T of the transmission-reception changeover switch 103, the mobile terminal 103C, the terminal 102b of the mode changeover switch 102, and the mobile terminal 102a, thereby being transmitted from the antenna 101.
The following is a description of the radio part of the TDD system. In FIG. 4 at the time of reception, the mobile terminal 102a of the mode changeover switch 102 and the mobile terminal 115C of the transmission-reception changeover switch 115 are connected to the terminal 102c and the terminal 115R, respectively. The high-frequency signal which has entered from the antenna 101 goes from the mobile terminal 102a of the mode changeover switch 102 to the terminal 102c, selects the transmission-reception frequencies of 1895.15-1917.95 MHz of its own station at the band filter 114, goes from the mobile terminal 115C of the transmission-reception changeover switch 115 to the terminal 115R, is amplified by the high-frequency amplifier 116, mixed with the local oscillation frequencies of 1635.15-1657.95 MHz which have been inputted by the converter 117 from the local oscillation unit 118 so as to be converted into an intermediate frequency of 260 MHz, demodulated by the demodulation unit 119, and as a result, a reception output is obtained.
At the time of transmission, the mobile terminal 115C of the transmission-reception changeover switch 115 is connected to the terminal 115T. The carrier frequency of 260 MHz is digital-modulated in the modulation signal generation unit 120 and converted into transmission frequencies of 1895.15-1917.95 MHz by using the frequencies of 1635.15-1657.95 MHz inputted from the local oscillation unit 118. After passing the band filter 121, the modulation signal is amplified by the high-frequency amplifier 122, passes the terminal 115T of the transmission-reception changeover switch 115, the mobile terminal 115C, the band filter 114, the terminal 102c of the mode changeover switch 102, and the mobile terminal 102a, thereby being transmitted from the antenna 101.
When the FDD mode is used, the control unit 114 so controls the mode changeover switch 102, transmission-reception changeover switch 103, local oscillation unit 107, demodulation unit 108, and modulation signal generation unit 109 that these operate in harmony with the above-mentioned frequency relationship in response to the transmission and reception. In the same manner, when the TDD mode is used, the control unit 114 so controls the mode changeover switch 102, transmission-reception changeover switch 115, local oscillation unit 118, demodulation unit 119, and modulation signal generation unit 120 that these operate in harmony with the above-mentioned frequency relationship in response to the transmission and reception.
Reception and transmission are time-shared by switching the transmission-reception changeover switch 103 in the FDD mode and the transmission-reception changeover switch 115 in the TDD mode at a much shorter frequency than an audio signal so as to perform transmission and reception at the same time.
The following is a description of a conventional TDD system dual band radio which is based on the TDMA system and can be used with two frequency bands. With reference to FIG. 5 which is a block diagram of the radio, the first frequency radio part will be described.
At the reception by the first frequency, the mobile terminal 132a of the band changeover switch 132 and the mobile terminal 134C of the transmission-reception changeover switch 134 are connected to the terminals 132b and 134R, respectively. The high-frequency signal which has entered from the antenna 131 goes from the mobile terminal 132a of the band changeover switch 132 to the terminal 132b, selects the transmission-reception frequencies of 940-956 MHz of its own station in the band filter 133, goes from the mobile terminal 134C of the transmission-reception changeover switch 134 to the terminal 134R, is amplified by the high-frequency amplifier 135, mixed with the local oscillation frequencies of 680-696 MHz which have been inputted by the converter 136 from the local oscillation unit 137 so as to be converted into an intermediate frequency of 260 MHz, demodulated by the demodulation unit 138, and as a result a reception output is obtained.
At the time of transmission, the mobile terminal 134C of the transmission-reception changeover switch 134 is connected to the terminal 134T side. The carrier frequency of 260 MHz is digital-modulated in the modulation signal generation unit 140 and converted into transmission frequencies of 940-956 MHz by using the frequencies of 680-696 MHz inputted from the local oscillation unit 137. After passing the band filter 141, the modulation signal is amplified by the high-frequency amplifier 142, passes the terminal 134T of the transmission-reception changeover switch 134, the mobile terminal 134C, the band filter 133, the terminal 132b of the band changeover switch 132, and the mobile terminal 132a, thereby being transmitted from the antenna 131.
The following is a description of the second frequency radio part. In FIG. 5 at the time of reception, the mobile terminal 132a of the band changeover switch 132 and the mobile terminal 144C of the transmission-reception changeover switch 144 are connected to the terminal 132c and the terminal 144R, respectively. The high-frequency signal which has entered from the antenna 131 goes from the mobile terminal 132a of the band changeover switch 132 to the terminal 132c, selects the transmission-reception frequencies of 1895.15-1917.95 MHz of its own station at a band filter 143, goes from the mobile terminal 144c of the transmission-reception changeover switch 144 to the terminal 144R, is amplified by the high-frequency amplifier 145, mixed with the local oscillation frequencies of 1635.15-1657.95 MHz which have been inputted by the converter 146 from the local oscillation unit 147 so as to be converted into an intermediate frequency of 260 MHz, demodulated by the demodulation unit 148, and as a result, a reception output is obtained.
At the time of transmission, the mobile terminal 144C of the transmission-reception changeover switch 144 is connected to the terminal 144T. The carrier frequency of 260 MHz is digital-modulated in the modulation signal generation unit 150 and converted into transmission frequencies of 1895.15-1917.95 MHz by using the frequencies of 1635.15-1657.95 MHz inputted from the local oscillation unit 147. After passing the band filter 151, the modulation signal is amplified by the high-frequency amplifier 152, passes the terminal 144T of the transmission-reception changeover switch 144, the mobile terminal 144C, the band filter 143, the terminal 132c of the band changeover switch 132, and the mobile terminal 132a, thereby being transmitted from the antenna 131.
When the first frequency is used, the control unit 139 so controls the band changeover switch 132, transmission-reception changeover switch 134, local oscillation unit 137, demodulation unit 138, and modulation signal generation unit 140 that these operate in harmony with the above-mentioned frequency relationship in response to the transmission and reception. In the same manner, when the second frequency is used, the control unit 139 so controls the band changeover switch 132, transmission-reception changeover switch 144, local oscillation unit 147, demodulation unit 148, and modulation signal generation unit 150 that these operate in harmony with the above-mentioned frequency relationship in response to the transmission and reception.
Reception and transmission are time-shared by switching the transmission-reception changeover switch 134 at the first frequency and the transmission-reception changeover switch 144 at the second frequency at a much shorter frequency than an audio signal so as to perform the transmission and reception at the same time.
In the FDD/TDD dual mode system shown in FIG. 4 the radio part of the FDD system comprises a transmission system and a reception system on the right side of the transmission-reception changeover switch 103, and in the same manner the radio part of the TDD system comprises a transmission system and a reception system on the right side of the transmission-reception changeover switch 115. Such a dual mode not only increases the production cost due to the complicated circuit structure, the increased number of components, and the time and labor of assembling but also prevents the miniaturization.
The TDD system dual band radio shown in FIG. 5 has the same problems, so that the simplification of the circuit structure has been demanded by sharing a circuit.